The question was just meant to illustrate why "Have you done MediaWiki core code development? "Importance" does not imply "a good place to start with"." is not addressing anything relevant. You keep going back to previous points and ignore what I'm saying maybe just calm a bit (not sure how you could even misunderstand it that way), have a good night of sleep and then read it again. I'll repeat it anyway:
However, that page is about developers new to M̶e̶d̶i̶a̶W̶i̶k̶i̶ (irrelevant I guess?) Wikipedia-related software development. Of those people only a fraction are new developers or not-yet-developers aspiring to become developers (many already are experienced devs). Partly because of that, I included the note "Development may be more difficult than with the projects below." A lot of the people may already be sufficiently experienced developers.
The inadequacy is even more apparent when outlining the process users come to this page: Wikipedia page->Developers->clicking "Choose a project" next to "Software development"->land on the "New Developers" page with not even a mention of the software that powers Wikipedia page.
Also that page doesn't even list a MediaWiki extension. And even if it did, that wouldn't remove the necessity to mention MediaWiki development.
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Basically, if you want to learn swimming and go to a page linked as "How to swim" you'd like it to contain info about swimming, not about how to walk. Yes, sure it may be easier to learn how to walk in your opinion but maybe, for example, you already can swim.